question on what pressure to charge tank

Hi,
i am new to the forum. I found this thread and it has been helpful. Ive got my shelf all ready for the tank install, but am getting nervous about the tank pressure.

A little background for ya: a couple of years ago the township flushed the hydrants and my water meter was damaged by some debris. I got it changed and honestly my water has never been 100% the same. I have the whistling shower heads, had a kitchen faucet leak on me and it got under my floating floor.

I tested several faucets (before the PRV change) and it the pressure was around 60 on the laundry sink (closest to the PRV).. it went down to 38 with another sink on and then 30 when the third sink was on.

after the PRV change, i am at 40 (24 hours).. but the red needle for the spike/highest level is at 90. i saw this happen before and it seemed to change when someone would use then shut another faucet off.

so my question is... do i set my tank pressure at the 40lbs? or should i adjust the prv up to about 50-55 and then set the tanks pressure at that psi?

sorry for so many questions. i am about 15 minutes from completing this job but dont want to do it with the wrong pressure setting.